Concern about the risk of pathological fractures in horses with pituitary pars intermedia dysfunction (PPID) prompted researchers to compare bone mineral density of weight-bearing and non-weight-bearing bones in PPID-positive horses compared to non-PPID controls.
Effects of Cortisol
There have been reports of spontaneous, pathological fractures of the mandible, coffin bone, pelvis, and ribs in horses with PPID. Glucocorticoids such as cortisol can have multiple effects:
- Inhibition of bone formation.
- Calcium absorption from the intestines.
- Increased bone resorption.
- Alterations in secretion of hormones, cytokines and bone growth factors.
The authors note that clinical signs of PPID are “attributed to actions of proopiomelanocortin (POMC)-derived peptides (such as adrenocorticotropic hormone), while cortisol excess has not been well-documented.” Yet, horses with PPID tend to be more prone to infection and experience poor wound healing, two issues that can be linked to cortisol excess.
PPID and Bone Mineral Density
The researchers examined five horses with PPID and compared results to six aged and four young non-PPID controls. They documented clinical signs and necropsy results for the lumbar vertebrae, the right front metacarpal bones (MC3), and the left hind cannon bones (MT3) following euthanasia. They quantified bone mineral density (BMD) using computed tomography of the bones’ trabecular and cortical regions.
The study authors reported no observable differences in BMD on CT images between PPID and non-PPID horses. However, quantitative analysis of the CT images demonstrated that the trabecular and cortical bone of lumbar vertebral bodies in PPID horses had lower BMD than the same vertebrae in the non-PPID controls regardless of age. In contrast, BMD did not differ between the hind or front weight-bearing cannon bones in PPID and non-PPID horses.
Final Thoughts
In summary, the authors state: “BMD of lumbar vertebrae, but not MC3 or MT3, from aged PPID-positive horses was found to be lower than that of aged PPID-negative horses. The lower BMD in PPID-affected horses could increase the risk of developing pathological fractures.”
Reference
Colbat AC, Fortin JS, Burglass C. Lumbar vertebral bone density is decreased in horses with pituitary pars intermedia dysfunction. Equine Veterinary Journal Dec 2023; DOI: 10.1111/evj.14039
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